In a brochure entitled “This is PLM Fosie” issued by Applicant's Swedish company PLM Fosie AB in the mid nineties, there is shown on p. 6 how can ends are produced.
In a first production stage, a thin metal strip, preferably a 0.23-mm-thick aluminum strip, is fed to a processing apparatus in which the strip is punched and stamped to form opening tabs integrated with the strip. The tabs are also referred to as opener rings by persons skilled in the art.
In a second production stage, circular shells for forming the can ends are die cut from a thin metal sheet, preferably a 0.23-mm-thick aluminum sheet. Each shell is scored for opening, and a rivet for attachment of the tab is formed at the center of the shell.
In a third production stage, the strip with the integrated tabs are joined with the circular shells in an attachment station, in which the tabs are separated from the strip and attached to the shells by riveting. A finished can end is achieved when the tab is fastened to the shell.
This manufacture of can ends is conventional and well known to the skilled person. It should be mentioned that the whole process is automated with a capacity of about 2,000 ends per line per minute. In the beverage can industry, the production rate in general is very high and it is a continuous aim to decrease the production costs and the material used for can production, including the ends. Maintenance, tool changes and other downtime should be avoided to keep costs low.
As in other areas of the food and beverage industry, the traceability of the manufacturing and filling of the can is important. Today, there are so-called traceability marks or markings on the cans indicating when the filling took place and also when the main can body was manufactured. Normally, however, there is no traceability marking indicating when the finished can ends were produced. Such markings are often required for reasons of quality. For instance, the peripheral edge of the shell must be precisely formed to ensure a completely tight seam against the upper flange of the can. There are also several functional requirements placed on the tab and on the attachment of the same to the shell.
Except for the purpose of indicating the origin of the tabs, the markings on the same may also be used in other contexts. In a commercial aspect, markings on the bottom surface of the tab may indicate the winner in a lottery or the like. The quality requirements on such “promotional” markings are normally the same as in the cases where the origin is indicated.
Thus, there is a need for indicative markings on the tabs and the shells as well as on the can body.
U.S. Pat. No. 4,459,910 discloses an arrangement for producing marked tabs from a continuous strip of metal. This arrangement comprises a press which, by a stamping and punching operation, shapes the strip into tabs to be included in cans. A feeder is arranged to intermittently feed the strip through the press at a rate commensurate with the operation of press. Markings are provided on a surface of the strip by means of an embossing machine arranged upstream of the press. The embossing machine comprises a plurality of embossing stamps arranged in an indexing wheel, so that different markings can be applied to the strip. Another machine for mechanically providing indicative markings on sheet metal by a stamping operation is disclosed in U.S. Pat. No. 4,476,781.
One general problem in using such stamping or embossing operations to provide small indicative markings on metal surfaces is that these surfaces should be non-coated for acceptable results. Thus, surfaces that are coated with lacquer and/or paint can not readily be provided with such markings. The task of providing markings on the tab is especially difficult, due to the small tab surfaces available and the high requirements of elevated production rate. For material saving reasons, modern opening tabs are quite small, inevitably leaving only very limited tab surfaces for markings at high speed. If such markings are to be provided by stamping operations or the like, the tab surfaces must be increased. However, a this calls for costly changes in the production equipment, increases the material cost and involves a risk of non-acceptance by the consumers. Further, the layout of “promotional” markings might be changed quite frequently, calling for frequent change of the tooling used for stamping the markings. Since such tooling is quite expensive, the cost for providing “promotional” markings can be considerable.